Modern air conditioning and refrigeration systems provide cooling, ventilation, and humidity control for all or part of an enclosure such as a building, a cooler, and the like. Generally described, the refrigeration cycle includes four basic stages to provide cooling. First, a vapor refrigerant is compressed within a compressor at high pressure and heated to a high temperature. Second, the compressed vapor is cooled within a condenser by heat exchange with ambient air drawn or blown across a condenser coil by a fan and the like. Third, the liquid refrigerant is passed through an expansion device that reduces both the pressure and the temperature of the liquid refrigerant. The liquid refrigerant is then pumped within the enclosure to an evaporator. The liquid refrigerant absorbs heat from the surroundings in an evaporator coil as the liquid refrigerant evaporates to a vapor. Finally, the vapor is returned to the compressor and the cycle repeats. Various alternatives on this basic refrigeration cycle are known and also may be used herein.
Traditionally, the heat exchangers used within the condenser and the evaporator have been common copper tube and fin designs. These heat exchanger designs often were simply increased in size as cooling demands increased. Changes in the nature of the refrigerants permitted to be used, however, have resulted in refrigerants with distinct and sometimes insufficient heat transfer characteristics. As a result, further increases in the size and weight of traditional heat exchangers also have been limited within reasonable cost ranges.
As opposed to copper tube and fin designs, recent heat exchanger designs have focused on the use of aluminum microchannel coils. Microchannel coils generally include multiple flat tubes with small channels therein for the flow of refrigerant. Heat transfer is then maximized by the insertion of angled and/or louvered fins in between the flat tubes. The flat tubes are then joined with a number of manifolds. Compared to known copper tube and fin designs, the air passing over the microchannel coil designs has a longer dwell time so as to increase the efficiency and the rate of heat transfer. The increase in heat exchanger effectiveness also allows the microchannel heat exchangers to be smaller while having the same or improved performance and the same volume as a conventional heat exchanger. Microchannel coils thus provide improved heat transfer properties with a smaller size and weight, provide improved durability and serviceability, improved corrosion protection, and also may reduce the required refrigerant charge by up to about fifty percent (50%).
Known copper fin and tube designs generally have issues with the possibility of galvanic corrosion. Such corrosion may be accelerated in the presence of water. Proper cleaning of the fin and tube designs thus was often difficult and time consuming. Reduced cleaning, however, could lead to reduced overall system efficiency because of debris trapped therein.
There is thus a desire for an improved microchannel heat exchanger design. Preferably such a microchannel heat exchanger could be routinely and quickly cleaned without the potential for galvanic corrosion or other types of damage or a lessened efficiency.